1. Field of the Invention
The present invention relates to a composition of a damping liquid to be enclosed in a hydraulic vibration-damping mount.
2. Description of the Prior Art
A hydraulic vibration-damping mount is composed of a vibration-damping rubber body adapted for supporting a vibrating body, which is provided with a liquid chamber therewithin, and is used to damp vibrations effectively by the operation of a damping liquid enclosed in the liquid chamber. One example of the above-described hydraulic vibration-damping mount is shown in FIG. 1.
In FIG. 1, the hydraulically vibration-damping mount is provided with vessel-shaped thick-walled vibration damping rubber body 1 having a lower opening, and a deformable rubber film 2 for closing the lower opening of the rubber body 1 to define a closed chamber. The closed chamber is filled with a damping liquid. The closed chamber is divided into an upper main liquid chamber A and a lower auxiliary liquid chamber B by a partition plate 3 having an orifice 31 at its center. The upper main liquid chamber A is defined by a wall of the vibration damping rubber body 1 while the lower auxiliary liquid chamber B is defined by a wall of the rubber film 2. Ordinarily, a liquid including ethylene glycol as a main ingredient is used as the damping liquid.
The hydraulic vibration-damping mount having the above-described construction is secured to a base body such as a vehicle frame through a vessel-shaped bottom plate 5 connected to a cylindrical side plate 4 adapted for supporting the vibration-damping rubber body 1. A vibrating body such as an engine is mounted on and secured to an upper plate 6, which is joined to a top surface of the vibration-damping rubber body 1.
When vibrations of large amplitude with frequency lower than that of the vibrating body are input, the vibration-damping rubber body 1 deforms to generate a high pressure within the main liquid chamber A. This causes the damping liquid to flow from the main liquid chamber A to the auxiliary liquid chamber B through the orifice 31 thereby generating a large vibration-damping force.
The walls defining the liquid chambers A, B conventionally have been made of natural rubber or natural rubber-based material cmposed of natural rubber and synthetic rubber such as styrene-butadiene rubber (SBR) or the like. The natural rubber or natural rubber-based material is superior to the other rubber material in vibration characteristics and durability, however it has a defect of in that it has low ozone resistance, accordingly, the hydraulic vibration-damping mount, especially the thin-walled rubber film 2 is apt to deteriorate due to ozone.
To prevent the vibration-damping mount from deteriorating due to ozone, a large amount of an age resistor having ozone resistance conventionally has been added to the rubber material. To this end, more than 10 parts by weight age (antiozonant) resistor must be added to 100 parts by weight rubber. This amount of the age resistor is much larger than the amount ordinarily added, which is only 1 through several parts by weight to the 100 parts by weight of rubber. This very large amount of age resistor is problematic in that the age resistor blooms on a surface of the rubber material when the mount is formed, blocking vulcanizing adhesion of the rubber material to the metallic member supporting the wall of the liquid chamber, thereby reducing the adhesive strength.